Mobile hydrogen-bonding donor in covalent organic framework for efficient iodine capture

Covalent organic frameworks (COFs) show promise for applications in molecule capture such as radioactive iodine (I2) capture, which is important in the development for nuclear energy and radiation medicine. However, fast and efficient I2 capture and release have remained insufficient for practical applications. Here, we demonstrated that mobile cationic hydrogen-bonding donor in nanochannel of anionic covalent organic framework (COFs) can promote the absorption and desorption of I2. The adsorption rate of COF Bmim-TpPaSO3 affording unfixed hydrogen-bonding donor 1-butyl-3-methylimidazolium ([Bmim]+) in the nanochannel reaches 2.86 g h-1, which is higher those of COF TpPa-SO3H (0.57 g h-1) with fixed hydrogen-bonding donor and COF TpPaSO3K without hydrogen-bonding donor. The adsorption capacity was also increased from 1.50 g g-1 to 5.25 g g-1. Experiments and quantum chemistry calculations show that introducing the hydrogen bond donor enhances the interaction of Bmim-TpPaSO3 with iodine and induces sulfonate ion of Bmim-TpPaSO3 to convert iodine molecules into polyiodide via charge-transfer mechanism. In addition, Bmim-TpPaSO3 has good recyclability and storage performance. This strategy has unlimited potential to significantly improve the performance of covalent organic framework materials in the field of gas adsorption.